In range-based location determination systems, time delay measurements of ranging signals from a plurality of sources are converted to range information associated with the source of each ranging signal. Ranges to different sources with known locations are combined to solve for the unknown user location via geometric techniques known, for example, as trilateration (a.k.a. triangulation). If the delay of ranging signals cannot be known reliably (e.g. in asynchronous systems where the user clock is not synchronized to the network), location determination algorithms may treat user clock temporal bias as another unknown, to be solved for by the trilateration process, using an additional ranging measurement.
In location determination systems, measured user distances to a plurality of sources with known locations are combined to solve for the unknown user location via geometric techniques, for example: advanced forward link trilateration (AFLT). AFLT typically requires that the number of measurements available be at least equal to the number of unknown coordinates in the system, including the mobile spatial coordinates and time bias. Additionally, several independent ranging signal measurements from a given terrestrial source may be available. As another example of this technique, multiple ranging signals from orbiting navigation satellites, such as GPS, GLONASS, and Galileo, may be used for location determination of a mobile user.
In previous location determination schemes, the ranging signal set is a selection of single ranging signal measurements from each source that are deemed most accurate via a predetermined threshold. Such schemes yield a single location determination solution from the ranging signal set of a single ranging signal measurement per source.
Using a single ranging signal measurement per source may result in degraded accuracy in location determination since the quality of the ranging signal measurements may have been corrupted by the presence of multipath interference (superposition of multiple versions of the same ranging signal received from different paths), fading (due to propagation path impairments) or other channel impairments (such as intermittent interference or random noise). Using multiple ranging signal measurements per source may improve the accuracy of the location determination solution. Multiple ranging signal measurements per source can be derived by measuring ranging signals from each source over different time intervals (i.e., temporal diversity), over different spatial offsets (i.e., spatial diversity) and/or over different frequencies (i.e., frequency diversity).
Accordingly, it is desirable to provide a method using temporal, spatial and/or frequency diversity for enhanced location determination to improve accuracy.